Winding for electromechanical transducers with coreless rotor

ABSTRACT

An electromechanical transducer has a coreless rotor winding formed of a series of loops, each of the loops having an active portion inclined to both the axial and tangential directions of the rotor and an inactive head portion oriented perpendicular to the axial direction. The relative length of the head portion of each loop affects the electrical characteristics of the transducer, such as starting torque, time constant and efficiency. By selecting the proper relative length for the head portion, the performance characteristics of the transducer may be optimized.

United States Patent [1 1 Faulhaber WINDING FOR ELECTROMECHANICALTRANSDUCERS WITH CORELESS ROTOR [75] lnventor: Fritz Faulhaber,

Schonaich(wurttembe g), Germany [73] Assignee: Retobobina Handelsanstalt[22] Filed: Feb. 7, 1973 211 App]. No.2 330,231

[30] Foreign Application Priority Data (111 3,793,548 1451 Feb. 19, 19743,360,668 12/1967 Faulhaber ..3l0/266X 3/1959 Germany 310/207 PrimaryExaminer-J. D. Miller Assistant Examiner-Mark O. Budd Attorney, Agent,or Firm--Benjamin 11. Sherman et al.

, [57] ABSTRACT Feb. 9, 1972 Austria 31034 An electromech ca a sduce a ao e ess rotor 521 US. Cl 310/266 310/154 310/207 winding fmmed a serieseach 310/208 310/268 having an active portion inclined to both the axialand 51 Int. Cl. H02k 23/30 1102k 23/32 tangential and an inactive head[58] Field of Search" 310/154 155 268 203 portion oriented perpendicularto the axial direction. 6 The relative length of the head portion ofeach loop affects the electrical characteristics of the transducer, [56]References Cited such as starting torque, time constant and efiiciency.By selecting the proper relative length for the head UNITED STATESPATENTS portion, the performance characteristics of the trans- 2,759,1168/1956 Glass 310/266 x ducer may be Optimized 3,191,081 6/1965 Faulhaber3,223,867 12/1965 Shapiro 310/206 X 10 Claims, 14 Drawing Figures 11 oL- 360 el Pmemw 91w 3.793548 QHEEY S UF 6 FIG. 7

. oh Mg PATENTE-fl FEB 1 9 1914 FIGJZ SHEU 6 [IF 6 WINDING FORE-LECTROMECHANICAL TRANSDUCERS WITH CORELESS ROTOR BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates tomechanical transducers, and more particularly to an improved windingarrangement therefor.

2. The Prior Art Two types of windings have been developed for corelessrotors of electromechanical transducers. One type, hereinafter referredto as a rectangular loop winding, is composed of closed loops formed ofactive portions oriented in parallel with the axial direction of therotor, and head portion oriented in parallel with the tangentialdirection, which is perpendicular to both the axial and radialdirections of the rotor. Such windings are il-,

lustrated and disclosed in German Patents No. 859,501 and No. 1,021,466.The second type of winding consists entirely of active portions whichare inclined to both the axial and tangential directions. Such windingsmay be either lap windings, as described in Czechoslovakian Patent No.486,150 or wave windings, as described in German Patent No. 1,188,709.Both wave windings and lap windings are customarily formed of one singlelength of wire, with taps for connection to a source of power providedwhere desired. Rectangular loop windings and lap windings are alsodescribed in my U.S. Pat. No. 3,467,847. I

The rectangular loop windings are best adapted for use with units havingstators with discrete rectangular poles in the magnetic circuit, whereasthe distributed lap and wave windings are better suited to a sinusoidalstator field distribution. Distributed windings which are withoutinactive head portions have the lowest possible winding resistance,because less wire is needed.

Although the winding types known in the prior art perform generallysatisfactorily, it is desirable to provide a winding arrangement whichimproves the electrical and mechanicalcharacteristics of the transducer.

SUMMARY OF THE INVENTION Accordingly, it is a principal object of thepresent invention to provide such an improved .win'ding arrangement. I

Another object of the present invention is to provide a windingarrangement by which higher starting torques may be obtained. A

A further object of the present invention is to provide a windingarrangement by which a smaller time constant may be obtained.

Another object of the present invention is to provide a windingarrangement by which a smaller figure for the weight-to-power ratio isobtained.

These and other objects and advantages of the present invention willbecome. manifest upon an examination of the following description andthe accompanying drawings.

In one embodiment of the present invention there is provided a windingfor an electromechanical transducer having loops with an active portioninclined to both the axial and tangential directions, and an inactivehead portion aligned with the tangential direction.

BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made to theaccompanyingin accordance with the so-called lap winding arrangement;

FIG. 3 is a plan view of a developed winding formed in accordance withthe so-called wave winding arrangement;

FIG. 4 is a plan view of three poles of a developed stator arrangement,including a graph illustrating the flux density in the space occupied bythe rotor;

FIG. 5 is a graph illustrating the flux density in the space adjacent adifferent stator arrangement;

FIG. 6 is a plan view of a developed winding formed in accordance withone embodiment of the present invention;

FIG. 7 is a plan view of a developed winding formed in accordance withanother embodiment of the present .invention;

FIG. 8 is a graph illustrating the relationship of certain parameters ofa winding formedin accordancewith the present invention;

FIG. 9 is a schematic illustration of the current flowing throughvarious portions of a winding constructed in accordance with the presentinvention;

FIG. 10a isa cross'section taken through a two pole transducer having astator arrangement for producing a sinusoidal field; 7 7

FIG. 10b is a cross-section taken through a four pole transducer havinga stator arrangement for'producing a pulse type field; I

FIG. 11 is a series of graphs illustrating the relation-' ship ofvarious parameters in a transducer incorporating the present inventionand having a stator arrangement like that shown in FIG. 10a;

FIG. I2 is a series of graphs illustrating the relationship of variousparameters in a transducer incorporating the present inventionand-having a stator arrangement like that shown in FIG. 10b; and 7 FIG.13 is a graph showing the relationship of efficiency to torque inatransducer incorporating the present invention, compared with oneemploying a prior art winding. I

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 3 illustrate threedifferent views of developed winding arrangements employed in the priorart. A developed winding is one which has been straightened from itsnormal circular-cylindrical configuration into a plane, for the purposeof illustrating the relationship of the various parts of the winding. InFIG. 1 the various loops of a rectangular loop winding have activeportions 10 which are parallel to the axial direction of the rotor, andinactive portions 11, which are parallel to the tangential direction ofthe rotor. The inactive portions 11 are hereinafter referred to aswinding heads. The winding heads are not active because they do notcross the magnetic flux produced by the stator field arrangement. Theflux, in a plan view of a developed winding. is aligned generally in adirection perpendicular to the plane of the paper.

The area in which the stator flux is effective is illustrated in FIGS.l-3 by a shaded area 100. The active portions of the windings passthrough the area 100, and a rotational force is produced by theinteraction of cur rent flowing through the winding and the magneticflux.

In FIGS. 2 and 3 no winding heads or inactive portions are included inthe windings shown; in each case, the entire winding is made up of aseries of loops having inclined portions 13, oriented at an angle to theaxial direction and also at an angle to the tangential direction of therotor. The winding illustrated in FIG. 2 is a lap winding, and thewinding'of FIG. 3 is a wave wind- The rectangular loop winding of FIG. 1is most suited to a stator pole arrangement which is shown in developedcondition in FIG. 4. The poles N and S are discrete elements havingrectangular cross-sections. A graph of the flux density B, along a lineparallel to the faces of the poles N and S in the space occupied by therotor, is illustrated in FIG. 4. The flux density B increases abruptlyto a positive value inthe space aligned with the north poles N andincreases abruptly to a negative value in the space aligned with thesouth pole S. The distance extending between centers of two adjacentpoles of the same polarity corresponds to 360 electrical degrees, asillustrated in FIG. 4.

FIG. 5 illustrates a graph of flux density produced by a differentstator arrangement, in relation to points along a line in the spaceoccupied by the rotor. The flux density B illustrated in FIG. 5 issinusoidal in shape, and

is most effective with windings of the type illustrated in FIGS.- 2 and3. However, coils constructed in accordance with the present inventionare more effective than any of the prior art coils illustrated in FIGS.1 to 3 in achieving an optimum combination of performancecharacteristics, as described more fully hereinafter.

A plan view of 360 electrical degrees of a developed windingincorporating the present invention is illustrated in FIG. 6. Thewinding of FIG. 6 is composed of loops, each of which has an activeportion 13 inclined to both the axial and tangential directions of therotor, and an inactive winding head portion 11, oriented in a directiongenerally aligned with the tangential direction. The shaded area 100shows the area of the stator flux. A section of one loop of the windingis also illustrated in FIG. 6, illustrating that the inactive portion 11is aligned generally in a tangential direction.

The winding of FIG. 6 is of the wave winding type in FIG. 7 a plan viewof a developed winding of the lap winding type is illustrated,incorporating another embodiment of the present invention. The windingof FIG. 7 incorporates inactive winding head portions 11 which arealigned generally in a peripheral direction relative to the rotor, whilethe inclined portions 13 are inclined to both the radial direction ofthe rotor and also to its tangential direction.

A winding constructed in accordance with the present invention, havingan inactive head portion 11 which is aligned with the tangentialdirection of the rotor, may be referred to as an inclined winding with awinding head or as a trapeze winding.

A feature of the present invention relates tothe length of the windinghead 11 in relation to the tip-totip length of the loop in thetangential direction. Varying the relative length of the winding head11, in relation to the tip'to-tip length of the loop, changes thecharacteristics of the transducer incorporating the winding, so that theoptimum parameters for a variety of circumstances may be produced, byselecting the appropriate length of the winding head 11 in relation tothe tip-to-tip length of each loop. I

FIG. 8 shows electrical degrees ofa single loop of a windingincorporated in the present invention. The winding may be similar tothat shown in FIG. 7, for example, in which case the upper left handquarter of a loop is represented in FIG. 8 by the lines 11 and 13,-

corresponding, respectively, to the inactive and active portions of theloop. The vertical scale indicates, on a scale from O to l, the height Hof the winding, as well as the current i and the flux density B. Thehorizontal scale indicates on a scale from 0 to l, the proportion of theinactive portion 11 to the loop length which, in the example of FIG. 8,extends over 90 electrical degrees, relative to the stator field. Thequarter loop of FIG. 8 has its portion 11 equal to 40 percent ofthe looplength, as shown by the upper scale. Beyond the portion illustrated inFIG. 8 the inclined portion 13 of the winding extends in the directionof an arrow 13] when it is a wave winding type, and it extends in thedirection of an arrow 132 when'it is a lap winding type. The stator fluxmay be either a sinusoidal type, 90 electrical degrees of which areillustrated by the curve 14, or a pulse type, 90 electrical degrees ofwhich are illustrated by the curve 15. g

If the relative length WKB of the winding head 11 is 0, the quarter loopbecomes a diagonal line 22, and the winding becomes a lap winding or awave winding. Similarly, if the relative length WKB of the winding head11 is unity, the winding becomes similar to the rectangular loop typewinding of FIG. 1. The present invention has aeonstruction in which therelative-winding head length WKB lies intermediate 0 to 1.

FIG. 9 is a schematic illustration of the current in a developed windingconstructed in accordance with the present invention, over360 electricaldegrees, resulting from connection to a current source at two pointsspaced electrical degrees apart. The connections to the current sourceare via lines 23 and 24, and are made via slip rings, a commutator, orthe like. In the zone 16 of FIG. 9, the resulting flow of current has adownward direction, as illustrated in FIG. 9, and in the zone 17 thecurrent has an upward direction. In both of the zones 16 and 17 there issome current which flows in the winding heads in a tangential directionand contributes nothing to the production of torque. The nature of thiscurrent is explained in greater detail in German Patent No. l,l88,709.

The graph illustrated in FIG. 8 can be employed to calculate certainparameters of the transducer including the time constant and thestarting torque. The starting torque is proportional to the product ofthe current 1' within the winding and the flux density B. In order tocalculate the force tending to rotate the coil which acts at a specificpoint on the circumference thereof, for example at the location 19 inFIG. 8, the incremental force is calculated by the relation:

T =fi( u/ wherein 1 represents the combined lengths of the inactivewinding-head 11 as well as the active portion 13, and f, is a functionsymbol.

The term (1),, is calculated from the flux (I) and the applied voltage Vby the relation:

The flux 4) is dependent upon the characteristics of the magneticcircuit of the stator of the transducer.

In FIGS. a and 10h embodiments of the present invention are illustrated,employing two different stator arrangements. The arrangement illustratedin FIG. 10a is primarily intended for a two pole machine, while thearrangement of FIG. 10b is primarily designed for a multi-pole machine.Both systems employ a surrounding ferromagnetic shield ER and magnets Mspaced inwardly from the outer shield ER. Accordingly, flux is producedin a gap between the outer shield ER and the interior parts of theapparatus, as conventional in the art. The rotor winding rotates in thisgap. The apparatus of FIG. 10a employs a single magnet M of circularconfiguration, while four magnets M are employed in the apparatus ofFIG. 10b, together with an interior ferromagnetic member ER to completethe magnetic circurt. I

In the apparatus of FIG. 10a, flux distribution in the air gap betweenthe shield ER and the magnet M is generally sinusoidal. For example, theflux density reaches a maximum along a horizontal line bisecting theapparatus of FIG. 10a, and a minimum along a vertical line bisecting theapparatus. The rotor, in making one complete revolution, thus passesthrough a complete cycle of sinusoidal flux density. In the apparatus ofFIG. 10b, the waveform of the flux density is rectangular in shape,reaching a maximum value at locations adjacent to the magnets M and aminimum between such locations.

When a winding constructed in accordance with the present invention isemployed with the apparatus of FIG. 10!), it is unnecessary to make thewinding head 11 any larger than the width of the magnet M. When theloops of the winding are approximately the same size as the area throughwhich the effective flux passes, virtually all of the effective flux islinked by the loops. However, it has been found that employing awinding, with a winding head 11 equal to the width of the magnet M doesnot give optimal results. On the contrary, it has been found that byemploying a winding head having a width which is smaller than the widthof the magnet M, better characteristics are obtained, as more fullydiscussed hereinafter.

Curves illustrating the characteristics of transducers employing thepresent invention are illustrated in FIGS. 11 and 12. In FIG. '11 thehorizontal axis is plotted on a scale of 0 to I in terms of WKB, which,as in FIG. 8, describes the relative length of the winding head, inproportionto the length of a winding loop. Accordingly, the curvesillustrated in FIG. 11 for WKB=0 give values for a transducer having acoil formed of inclined windings such as shown in FIGS. 2 and 3. As theWKB dimension increases, the change in the parameters is illustrated inFIG. 11. The curves of FIG. 11 hold for the sinusoidal systemillustrated in FIG. 10a and the curves of FIG. 12 hold for the pulsetype stator arrangement illustrated in FIG. 10b.

The curves of FIG. 12 are plotted on the same scale, namely in terms ofthe relative winding head length WKB on a scale from 0 to l. The curveR0 in FIG. 12 illustrates that the resistance R0 of the winding risesfrom a minimum at WKB=0 to a maximum at WKB=I. Nevertheless, in spite ofthe rising resistance, the starting torque rises as the WKB dimension isincreased from 0, as shown by the curves in FIG. 11. The starting torquecurves are designated Md and four such curves are illustrated in FIG.II, in accordance with the length ofa loop ofthe winding in relation tothe tangential distance between adjacent poles of the stator field. Thisis indicated in FIG. I] by the parameter MB. When MB=I, the loop lengthis the same as the distance between adjacent poles of the stator field.When MB=0.25, the coil length is equal to one-fourth of the distancebetween poles of the stator field. For an MB of between 0.50 and 0.75,the starting torque Md reaches a maximum when the winding head length isapproximately one-half of the total length of the loop,

giving a WKB equal to 0.5. This value is somewhat dependent on thelength (and therefore the height H) of the winding. Nevertheless itremains in about the same relation to the time constants as isillustrated in FIG.

The time constants r for the four different values of MB are alsoillustrated in FIG. I I. The minimum values for the time constants whenMB is approximately.0.50 to 0.75 occurs at about the same value of WKBas the maximum starting torques. For higher values of WKB, the conditionbecomes worse, with decreasing starting torques and higher timeconstants. In addition, transducers having higher values of WKB increasein size due to the increased length of the winding head, and the weightof the transducer increases accordingly. It is therefore desirable tochoose a compromise value of WKB, where size and weight are tolerable,and the starting torque and time constant are improved.

The curves in FIG. 12, which hold for multi-polar machines havingindividual magnets, illustrate that although the resistance of thewinding increases as the WKB parameter increases, the starting torque Mdhas a maximum at approximately WKB=0.5, and the time constant reaches aminimum at a higher value of WKB. The curves of FIG. 12 are shown forone value of MB,

but it is understood that the. variation of MB resultsin I differentcurves such as are illustrated in FIG. II.

For machines constructed in accordance with FIG. 10b, it is necessary totake into consideration the magnet width, meaning the tangentialdimension of the magnet M. In general a magnet width of an entire poledivision (in which MB=1) is not practical, for then the leakage betweenadjacent magnets short circuits the greater part of the flux.Accordingly, the magnet widths must be less than I and are preferablyabout 0.8 the distance between poles.

The starting torque Md has a distinct maximum and the time constant 1-hasa distinct minimum at another value of WKB in FIG. 12. Accordingly,if a transducer with maximum starting torque is desired, WKB is chosenat about 0.5, while, if a minimum time constant is desired, a WKB valueof 0.7 is chosen.

If it is desired to design a transducer with an especially low weight,rather than attempting to minimize the time constant or maximize thestarting torque, then smaller magnet widths W' are selected. As thecrosssection of the magnet is smaller, the cross-section of theferromagnetic shield ER may also be smaller, which appreciably reducesthe size and weight of the transducer.

The selection ofdifferent magnet widths does not appreciably affect theheat-emitting surface of the transducer so that, for a given magnetwidth, if the parameters of the winding are optimized, an optimaltransducer may be designed.

By employing the curves of FIGS. ll and 12, and others like them forother values of MB, it is possible to design in each case an optimumtransducer for the design required, by choosing an appropriate relativelength of the winding head. The important factors to be taken intoconsideration in arriving at such a design are the armature resistance Rthe starting torque M41 the time constant 1, the weight per unit power,etc.

In the past only the number ofturns in a winding, and the size of thewire employed therefor, have been varied in attempting to reach anoptimum design for a particular application. By means of the presentinvention the relative length of the winding head may also be varied,thus permitting a substantially better solution for any given set ofdesign parameters. The advantages of using the present invention in sucha case, is that the time constant is improved and the starting torque isimproved, as compared with prior art windings.

As the relative length of the winding head is in creased, the totallength of the winding is also increased, so that for a given current thei R losses increase with the length of the winding. l-IOwever, theincrease in resistance increases more slowly than the increase in thetorque, so that when the present invention is employed to produce agiven torque, there is a lower heat loss because less current isrequired to develop the required torque. This factor is illustrated inFIG. 13, in which the efficiency '1; is plotted against the torque Mddeveloped by the transducer. The curve is for a transducer employing oneof the prior art Windings whereas the dashed line curve 21 is for atransducer incorporating the present invention. The maximum efficiency,which is reached at relatively low torque, is equal for both systems.However, at other torques, the winding constructed in accordance withthe present invention has a higher efficiency than achieved by theprevious windings.

Although the taps, by which current is supplied to the windings, havenot been shown in the drawings referred to above, it will be understoodthat the windings are tapped in the same way as is conventional in theart, and that such taps are brought to a location outside the transducerby means of slip rings, commutators, or the like.

A winding incorporated in the present invention is usable not only withmotors and generators, but also with prime movers whose armatures do notrotate in complete revolutions, such as in measuring devices, forexample. The present invention may also be employed when the rotor andthe stator exchange their roles in the known manner, and the windingdescribed herein is stationary while the magnetic field generatingsystem rotates about the stationary winding.

Although the winding heads 14 have been shown as being oriented in atangential direction, they may also be constructed to have a radialcomponent, so as to form chords at the axial ends of the windings.Windings constructed in accordance with the present inventions may beeither distributed, by being wound from a single length of wire, oralternatively they may he formed as individual loops.

What is claimed is:

1. In an electromechanical transducer having means for generating amagnetic field and a coreless rotor adapted to rotate through saidfield, a winding for said rotor comprising a plurality of loops, each ofsaid loops having an active portion inclined to the axial direction ofsaid rotor and inclined to the tangential direction of said rotor and aninactive winding head portion oriented generally perpendicularly to saidradial direction.

2. The winding according to claim 1, wherein said winding head portionis oriented generally in a tangential direction.

3. The winding according to claim 1, wherein said winding head portionhas a tangential length greater than 0.4 of the tangential length of oneof said loops.

4. The winding according to claim 3, wherein said winding head portionhas a tangential length less than 0.7 of the tangential length of one ofsaid loops.

5. The winding according to claim 1, wherein said loops are formed asindividual loops.

6. The winding according to claim 1, wherein said loops are formed of asingle length of wire.

7. In an electromechanical transducer having means for generating amagnetic field and a coreless rotor adapted to rotate through saidfield, a winding for said rotor comprising a plurality of loops, each ofsaid loops having an active portion inclined to the axial direction ofsaid rotor and inclined to the peripheral direction of said rotor and aninactive winding head portion connected with said active portion, saidwinding head portion having a tangential length of between 0.4 and 0.7of the length of said loop.

8. In an electromechanical transducer having means for generating amagnetic field and a coreless rotor adapted to rotate through saidfield, a winding for said rotor comprising a plurality .of loops, eachof said loops having an active portion inclined to the axial directionof said rotor and inclined to the peripheral direction of said rotor andan inactive winding head portion connected with said active portion,said winding head portion having a tangential length of between 0.4 and0.7 of the distance between two points separated by electrical degreesof said field.

9. In an electromechanical transducer having means for generating amagnetic field, the combination comprising a winding located within saidfield, and means for rotating said magnetic field relative to saidwinding, said winding having a plurality of loops, each of said loopshaving an active portion inclined to the axial direction of said rotorand inclined to the tangential direction of said rotor and an inactivewinding head portion, said winding head portion being oriented generallyperpendicularly to said radial direction.

10. Apparatus according to claim 9, wherein said means for rotatingcomprises means for supporting said winding and means for rotating saidfield generating means.

1. In an electromechanical transducer having means for generating amagnetic field and a coreless rotor adapted to rotate through saidfield, a winding for said rotor comprising a plurality of loops, each ofsaid loops having an active portion inclined to the axial direction ofsaid rotor and inclined to the tangential direction of said rotor and aninactive winding head portion oriented generally perpendicularly to saidradial direction.
 2. The winding according to claim 1, wherein saidwinding head portion is oriented generally in a tangential direction. 3.The winding according to claim 1, wherein said winding head portion hasa tangential length greater than 0.4 of the tangential length of one ofsaid loops.
 4. The winding according to claim 3, wherein said windinghead portion has a tangential length less than 0.7 of the tangentiallength of one of said loops.
 5. The winding according to claim 1,wherein said loops are formed as individual loops.
 6. The windingaccording to claim 1, wherein said loops are formed of a single lengthof wire.
 7. In an electromechanical transducer having means forgenerating a magnetic field and a coreless rotor adapted to rotatethrough said field, a winding for said rotor comprising a plurality ofloops, each of said loops having an active portion inclined to the axialdirection of said rotor and inclined to the peripheral direction of saidrotor and an inactive winding head portion connected with said activeportion, said winding head portion having a tangential length of between0.4 and 0.7 of the length of said loop.
 8. In an electromechanicaltransducer having means for generating a magnetic field and a corelessrotor adapted to rotate through said field, a winding for said rotorcomprising a plurality of loops, each of said loops having an activeportion inclined to the axial direction of said rotor and inclined tothe peripheral direction of said rotor and an inactive winding headportion connected with said active portion, said winding head portionhaving a tangential length of between 0.4 and 0.7 of the distancebetween two points separated by 180 electrical degrees of said field. 9.In an electromechanical transducer having means for generating amagnetic field, the combination comprising a winding located within saidfield, and means for rotating said magnetic field relative to saidwinding, said winding having a plurality of loops, each of said loopshaving an active portion inclined to the axial direction of said rotorand inclined to the tangential direction of said rotor and an inactivewinding head portion, said winDing head portion being oriented generallyperpendicularly to said radial direction.
 10. Apparatus according toclaim 9, wherein said means for rotating comprises means for supportingsaid winding and means for rotating said field generating means.